The Duchess of Cambridge is pregnant with her second baby, Kensington Palace has announced.

Prince William and Kate said they were "very pleased to announce" that they are expecting their second child.

It comes a year and two months after she gave birth to Prince George at St Mary's Hospital in London.

Sky's Royal Correspondent Paul Harrison says he has been told by Kensington Palace that the Duchess is not yet 12 weeks into her pregnancy.

Image:The Duchess pictured during one of her most recent engagements in August

The Duke of Cambridge said they were "immensely thrilled", but added it had been "a tricky few days".

Kate is suffering from severe morning sickness, as she did with her first pregnancy.

Speaking at a planned engagement in Oxford which Kate was unable to attend, William said: "She's feeling okay.

"It's great news - early days, but I'm hoping things will settle down and she feels a bit better... I've got to get back and look after her now."

Doctors are understood to be treating her at Kensington Palace, where she has an apartment with Prince William.

Video:Duchess Expecting A Second Baby

William said the Duchess may be over the worst of her morning sickness in a "few weeks' time".

The palace said the Queen and members of both William and Kate's families are "delighted".

Prince Harry, speaking at the Invictus Games, said it was "exciting" and joked that he could not wait for his brother to "suffer more" with another child.

Video:Prince George: His First Year

The couple's second child will become fourth in line to the throne, moving Prince Harry to fifth in the line of succession.

When it was put to him that the new baby further reduced his own chances of becoming King, Harry laughed and said: "Great!"

When she suffered from the condition called Hyperemesis Gravidarum during her last pregnancy, she had to be admitted to the King Edward VII Hospital in central London.

Her admission to hospital at the time brought forward the announcement that she was pregnant.

Although she had not reached the 12-week mark - when it is most typical to make a pregnancy public - palace officials are understood to have realised they would be unable to conceal her condition.

Prime Minister David Cameron released a statement moments after the announcement, saying: "Many congratulations to the Duke and Duchess of Cambridge. I'm delighted by the happy news that they're expecting another baby."

Labour leader Ed Miliband said on Twitter: "Fantastic to hear that Prince George will soon be a big brother! Congratulations to the Duke and Duchess of Cambridge on their happy news."

Scottish Nationalist Party leader Alex Salmond also tweeted his congratulations, referring to the royal couple by their Scottish titles.

He said: "Congratulations & best wishes to the Earl & Countess of Strathearn. Wonderful to hear they're expecting their second baby - very happy news!"

The names that are the betting companies' favourites so far are Arthur, Diana and Victoria (10-1), according to Sky Bet.

Kensington Palace said the attendance by the Duchess at future engagements, including a forthcoming solo trip to Malta, would be decided on a "case-by-case" basis.